This invention relates generally to jet propulsion engines, and more specifically to adaptive core engines and methods of operating them under variable flow conditions while maintaining near constant overall pressure ratio.
Future mixed mission morphing aircraft as well as more conventional mixed mission capable military systems that have a high value of thrust/weight ratio present many challenges to the propulsion system. They need efficient propulsion operation at diverse flight speeds, altitudes, and particularly at low power settings where conventional engine designs may have reduced part-power efficiency.
When defining a conventional engine cycle and configuration for a mixed mission application, compromises have to be made in the selection of fan pressure ratio, bypass ratio, and overall pressure ratio to allow an engine to operate effectively at both subsonic and supersonic flight conditions. In particular, the fan pressure ratio and related bypass ratio selection needed to obtain an engine capable of developing the thrusts needed for combat maneuvers and supersonic operation are non-optimum for efficient low power subsonic flight where conventional design engines cannot retain the high overall pressure ratio.
In the art, the core concepts studied in multi-core engines are quite complex, having multiple cores with multiple compressors. The transition of operation between these multiple compressors would require the use of complex diverter ducts and valves. Further, the engines may be required to operate at any operating point during transitions from the high-power mode to the low-power mode or vice-versa. Further, operation of the engine near or at minimum SFC (Specific Fuel Consumption) levels is desirable at any intermediate point. It is desirable that the engine should not be operated at an overall pressure ratio higher than that of the high-power mode because of cooling air restrictions on compressor exit temperature.
Accordingly, it would be desirable to have an adaptive core engine having a simple core design having the variable flow-near constant pressure ratio operating capability while retaining more traditional framing, sealing, and bearing designs. It would be desirable to have a method of operating multiple compressor blocks in an adaptive core engine whereby the adaptive core engine transitions between high power mode and a low power mode and substantially maintains an overall high pressure ratio in both modes without creating reverse flows in bypass ducts.